Valve Mechanism and Mechanical Lash Adjuster

TECHNICAL FIELD

The present invention relates to a valve mechanism automatically adjusting a valve clearance (e.g., a gap between a cam and a rocker arm in a rocker-arm valve mechanism or a gap between a cam and a tappet (bucket) covering a stem in a direct-acting valve mechanism) and a mechanical lash adjuster used in the valve mechanism.

BACKGROUND ART

It is widely known that when an intake valve or an exhaust valve used in an engine of an automobile etc. is mounted on an intake port or an exhaust port of a cylinder head, for example, a rocker arm linked to a stem is configured to swing by using a mechanical lash adjuster as a fulcrum, so as to automatically adjust a valve clearance through driving (extension/contraction motion) of the mechanical lash adjuster (e.g., see Patent Documents 1, 2, and Non-Patent Literature 1).

This type of the mechanical lash adjuster includes a plunger (pivot member) having a male thread formed on the outside and a cylindrical housing that is a plunger engaging member having a female thread formed on the inside, and has a structure in which the male thread on the outside of the plunger is screwed into the female thread on the inside of the housing to form a thread engagement portion and a plunger spring (compression coil spring) is housed in the housing such that the plunger spring urges the plunger toward a rocker arm on the upper side. By setting angles (lead and flank angles) of “thread ridges” of “buttress threads” made up of the female thread on the housing side and the male thread on the plunger side to predetermined angles, the plunger is allowed to slide and rotate in the thread engagement portion and thereby moved in a direction in which the plunger projects from the housing (hereinafter referred to as a “plunger extension direction”) under an axial load in the same direction, while the slide rotation of the plunger is suppressed in the thread engagement portion (hereinafter, this will be referred to as “threads” being made self-sustaining) by a friction generated in the thread engagement portion in a direction in which the plunger sinks into the housing (hereinafter referred to as a “plunger contraction direction”) under an axial load in the same direction, and the valve clearance is thereby automatically adjusted.

PRIOR ART DOCUMENTS
Patent Documents

Patent Document 1: Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 61-502553 (FIGS. 1 to 5)

Patent Document 2: Japanese Unexamined Utility Model Application Publication No. 3-1203 (FIGS. 1 to 3)

Patent Document 3: WO2013-136508A

Non-Patent Literature

Nonpatent Literature 1: NTN TECHNICAL REVIEW No. 75 (2007), Article “Development of the End-Pivot Type Mechanical Lash Adjuster” (pp. 78-85, FIGS. 1 to 4)

SUMMARY OF THE INVENTION
Problem to be Solved by the Invention

However, while the conventional mechanical lash adjusters (Patent Documents 1, 2, and Non-Patent Document 1) can operate in the direction of reducing the valve clearance (the plunger extension direction) when the valve clearance is increased, the mechanical lash adjusters have no adjust structure actively increasing the valve clearance (adjusting the valve clearance to zero) in the operation in the direction of increasing the valve clearance (the plunger contraction direction) when the valve clearance is reduced, although having a margin for adjustment of thread backlash (backlash).

Therefore, for example, if the engine is rapidly cooled after being stopped in a warmed state, the valve clearance may be put into an excessively small (negative clearance) state due to a difference in thermal expansion coefficient between a cylinder head (aluminum alloy) and a valve (iron alloy) so that a face surface of the valve may float from a valve seat, and in such a situation, since the conventional lash adjusters cannot operate in the plunger contraction direction (direction of increasing the valve clearance), the excessively small (negative clearance) state of the valve clearance is left as it is, leading to a risk of an excessing valve lift amount or defective sealing between the face surface of the valve and the valve seat (sealing of a combustion chamber) when the engine is restarted while being cold.

Therefore, in consideration of the problem described above, as described in Patent Document 3, the present inventors made a proposition that by setting a lead angle and a flank angle of thread ridges of “threads” constituting a thread engagement portion (e.g., setting the lead angle and the flank angle to ranges of 10 to 40 degrees and 5 to 45 degrees, respectively), the plunger is allowed to slide and rotate in the thread engagement portion and moved in an axial-load acting direction when an axial load acts on the plunger in either of extension and contraction directions and, if the sum of friction torques respectively generated on sliding contact surfaces of the plunger with an axial-load transmitting member (such as a rocker arm) and the plunger spring exceeds a thrust torque causing the plunger to slide and rotate in the thread engagement portion, the threads of the thread engagement portion are made self-sustaining (the slide rotation of the plunger is suppressed in the thread engagement portion and the plunger is made immovable in the thread engagement portion).

However, the present inventors continued experiments to find that when the mechanical lash adjuster according to Patent Document 3 is used, the following new problem occurs although the problem described above is solved.

Specifically, in the excessively small state of valve clearance generated if the engine is rapidly cooled after being stopped in a warmed state or the valve seat surface is worn out, when it is supposed that the plunger should sink so as to eliminate the excessively small state of valve clearance by a proper amount to a predetermined position at which the sum of friction torques respectively generated on the sliding contact surfaces of the plunger with the axial-load transmitting member (such as a rocker arm) and the plunger spring exceeds the thrust torque causing the plunger to slide and rotate in the thread engagement portion, the plunger sinks more than the proper amount, causing an unexpected state (new problem) in which a ramp portion (a portion adjusting acceleration of a valve) between a base circle and a cam nose of a cam fails to function, resulting in a hitting noise of the cam nose hitting the axial-load transmitting member or a collision noise of a face surface (seat) of a head colliding with a valve seat insert.

As a result of studies by the present inventors on the cause thereof, it was found that while a backlash (clearance between male and female threads) is always provided between the male and female threads constituting the thread engagement portion, this backlash is the cause of the “excessive sinking amount of the plunger”.

Specifically, for example, in a rocker-arm valve mechanism in which a pressing force of a cam acts on a plunger via a rocker arm, when a contact point between the cam and the rocker arm moves on the rocker arm, in addition to an axial load along the axis of the plunger, a lateral load (see reference numerals T1, T2 of FIG. 5) acts on the plunger in a lateral direction relative to the axis due to a change in the acting direction of the pressing force of the cam. When this lateral load acts on the plunger, the plunger swings in the lateral-load acting direction by an amount corresponding to the backlash (the gap between the male and female threads) of the thread engagement portion and, since the plunger moves in the axial-load acting direction while sliding and rotating due to this swing of the plunger, the plunger sinks more than an assumed sinking amount.

Regarding this new problem, if the backlash of the thread engagement portion is made as small as possible so that the influence of the lateral load acting on the plunger can be ignored, i.e., if the backlash is so small that no moment occurs in the thread engagement portion due to the swing of the plunger, the sinking amount of the plunger in the thread engagement portion becomes proper, and the lash adjuster appropriately operates to eliminate the excessively small state of the valve clearance. However, it is extremely difficult to perform threading of the male and female threads constituting the thread engagement portion such that the backlash becomes small, and it is substantially difficult to guarantee constant quality of mass-produced lash adjusters.

The present invention was conceived in view of the situations and a first object thereof is to provide a valve mechanism capable of automatically and reliably adjusting a valve clearance.

A second object is to provide a mechanical lash adjuster used in the valve mechanism.

Means for Solving Problem

To achieve the first object, the following configurations (1) to (6) are employed.

(1) In a valve mechanism comprising a cam rotating in conjunction with rotation of an engine output shaft; a shaft end portion of a valve urged in a valve closing direction by a valve spring; a power transmitting member interposed between the shaft end portion of the valve and the cam to transmit a pressing force of the cam to the shaft end portion of the valve as a valve opening force; and a mechanical lash adjuster linked to the power transmitting member and adjusting a valve clearance between the cam and the power transmitting member,

the mechanical lash adjuster includes

a plunger that is brought into contact with the power transmitting member and to which the pressing force of the cam and an urging force of the valve spring are transmitted through the power transmitting member,

a plunger engaging member that is put into thread engagement with the plunger to form a thread engagement portion cooperating with the plunger to extend and contract the plunger based on rotation relative to the plunger and that is retained non-rotatably in a circumferential direction of the thread engagement portion, and

a compression coil spring associated with the plunger and the plunger engaging member and urging the plunger in a direction in which the power transmitting member comes into contact with the cam, and

the thread engagement portion is set such that when a load acts on the plunger in one of extension and contraction directions of the plunger, slide rotation of the plunger relative to the plunger engaging member is suppressed in the thread engagement portion by a friction torque generated in the thread engagement portion and that when a lateral load acts on the plunger to cause a swing of the plunger relative to the plunger engaging member, the suppression of the slide rotation is relieved.

According to this configuration, due to the setting of the thread engagement portion, when the axial load acts on the plunger as a load in one of extension and contraction directions, the thread engagement portion becomes relatively immovable (threads are made self-sustaining), and a drive force according to the rotation of the cam is transmitted to the power transmitting member. Therefore, the valve can properly be operated to open and close by utilizing the power transmitting member (when the power transmitting member is a rocker arm, the plunger functions as a fulcrum for swinging the rocker arm).

On the other hand, when a lateral load acts on the plunger, the plunger operates by an amount equivalent to a backlash of the thread engagement portion in the acting direction of the axial load to the plunger (a plunger extension direction (direction of decreasing the valve clearance) or a plunger contraction direction (direction of increasing the valve clearance)) so that the valve clearance is adjusted, and the adjustment of the valve clearance is implemented by utilizing only the slide rotation of the plunger due to the swinging of the plunger in the lateral-load acting direction based on the backlash without utilizing the structure causing the plunger to slide and rotate due to the action of the axial load to the plunger (the structure of Patent Document 3). Therefore, unlike the case that the valve clearance is adjusted by the structure allowing the axial load to act on the plunger to cause the slide rotation of the plunger, the plunger is prevented from moving more than an assumed movement amount. Consequently, the valve clearance can automatically and reliably be adjusted.

Although the lash adjuster is configured such that when the axial load acts on the plunger in either of extension and contraction directions, the slide rotation of the plunger is suppressed in the thread engagement portion by a friction torque generated in the thread engagement portion, since the lash adjuster is configured to cause the plunger to slide and rotate in the thread engagement portion by actively utilizing the fact that the plunger swings due to the lateral load by an amount corresponding to the backlash of the thread engagement portion, it is not necessary to make the backlash of the thread engagement portion smaller than the conventional backlash, and the threading of the male and female threads constituting the thread engagement portion is accordingly made easier. Therefore, the present invention is extremely effective for mass-production of mechanical lash adjusters with constant quality guaranteed.

(2) Under the configuration of (1),

a torsion spring is associated with the plunger and the plunger engaging member so that the plunger is urged in a relative rotational direction for extension from the plunger engaging member.

According to this configuration, even when the structure as described above (the valve mechanism described in (1)) is implemented as the valve mechanism and an engine is sequentially cold-started, stopped, and cold-restarted, an abnormal noise can be prevented from occurring based on collisional contact of the cam with the power transmitting member.

In particular, when the engine is cold-started, the valve becomes extended due to a high-temperature exhaust gas for catalytic activation and the valve clearance is going to be in the excessively small (negative clearance) state and, therefore, to make an adjustment to a proper valve clearance, the plunger deeply enters the plunger engaging member (the plunger contraction state) and eliminates the excessively small state of the valve clearance.

However, when the engine is stopped in the above state, the state of suppressing the slide rotation is maintained in the thread engagement portion and the plunger is retained in the state of having deeply entered the plunger engaging member, so that when the engine is subsequently restarted while being cold, the valve has contracted and returned to the original state and, on the other hand, the above state (the state of the plunger having deeply entered the plunger engaging member) is maintained, and therefore, although the plunger attempts to extend so as to make an adjustment to a proper valve clearance, the plunger cannot extend unless a lateral load acts on the power transmitting member due to the rotation of the cam, so that the plunger may not promptly return to the properly extended state. Consequently, when the base circle of the cam faces the power transmitting member in the above case, the clearance between both becomes excessively large, and the cam collisionally comes into contact at an open ramp portion thereof with the power transmitting member and makes an abnormal noise.

Therefore, with the configuration in which a torsion spring is associated with the plunger and the plunger engaging member so that the plunger is urged in a relative rotational direction for extension from the plunger engaging member, the plunger is extended based on the urging force of the torsion spring as long as the valve clearance exists and, when the base circle of the cam faces the power transmitting member at the time of restart, the base circle is always in contact with the power transmitting member. Consequently, even when the structure as described above is implemented as the valve mechanism and the engine is sequentially cold-started, stopped, and cold-restarted, the abnormal noise can be prevented from occurring based on collisional contact of the cam with the power transmitting member.

(3) Under the configuration of (2),

the compression coil spring and the torsion spring are constituted as a plunger spring by one spring member.

According to this configuration, while the same effects as (2) described above can be implemented, the parts count of the spring members implementing the effects can be reduced and the disposition space for arranging the spring members can be made as small as possible.

(4) Under the configuration of (2),

the compression coil spring and the torsion spring are separately independently provided as a plunger spring.

According to this configuration, the compression coil spring and the torsion spring are individually selected from the viewpoint of the spring coefficient etc., and the springs in the valve mechanism can easily be adjusted in terms of the urging force.

(5) Under the configuration of (1),

the plunger engaging member is a cylindrical housing retained by a cylinder head,

the plunger has one end of the plunger as a contact end for the power transmitting member and is arranged such that one end side of the plunger projects from the housing while the other end side of the plunger other than the one end side is housed in the housing, and

the thread engagement portion is constituted by a male thread formed on an outer circumferential surface of the plunger and a female thread formed on an inner circumferential surface of the housing and screwed with the male thread.

According to this configuration, a mechanism having a specific and preferable structure can be provided as the valve mechanism.

(6) Under the configuration of (1),

the thread engagement portion is set such that due to a lead angle and a flank angle of thread ridges of the threads constituting the thread engagement portion, when a load acts on the plunger in one of extension and contraction directions of the plunger, slide rotation of the plunger relative to the plunger engaging member is suppressed in the thread engagement portion by a friction torque generated in the thread engagement portion and that when a lateral load acts on the plunger to cause a swing of the plunger relative to the plunger engaging member, the suppression of the slide rotation is relieved.

According to this configuration, the action of (1) described above can be specifically be implemented by utilizing the characteristics of the lead angle and the flank angle of the thread ridges of the “threads” constituting the thread engagement portion.

To achieve the second object, the following configurations (7) to (13) are employed.

(7) In a configuration comprising

a plunger;

a plunger engaging member put into thread engagement with the plunger to form a thread engagement portion cooperating with the plunger to extend and contract the plunger based on rotation relative to the plunger; and

a compression coil spring associated with the plunger and the plunger engaging member and urging the plunger in a direction in which the plunger is extended relative to the plunger engaging member,

According to this configuration, a preferable mechanical lash adjuster used in the valve mechanism of (1) can be provided.

(8) Under the configuration of (7),

a torsion spring is associated with the plunger and the plunger engaging member so that the plunger is urged in a relative rotational direction for extension from the plunger engaging member.

According to this configuration, a preferable mechanical lash adjuster used in the valve mechanism of (2) can be provided.

(9) Under the configuration of (8),

the compression coil spring and the torsion spring are constituted as a plunger spring by one spring member.

According to this configuration, a preferable mechanical lash adjuster used in the valve mechanism of (3) can be provided.

(10) Under the configuration of (8),

the compression coil spring and the torsion spring are separately independently provided as a plunger spring.

According to this configuration, a preferable mechanical lash adjuster used in the valve mechanism of (4) can be provided.

(11) Under the configuration of (7),

the plunger engaging member is a cylindrical housing,

the plunger is arranged such that one end side of the plunger projects from the housing while the other end side of the plunger other than the one end side is housed in the housing, and

According to this configuration, a preferable mechanical lash adjuster used in the valve mechanism of (5) can be provided.

(12) Under the configuration of (7),

the configuration is used in a valve mechanism including a cam rotating in conjunction with rotation of an engine output shaft, a shaft end portion of a valve urged in a valve closing direction by a valve spring, and a power transmitting member interposed between the shaft end portion of the valve and the cam to transmit a pressing force of the cam to the shaft end portion of the valve as a valve opening force, for adjusting a valve clearance between the cam and the shaft end portion of the valve,

the plunger is brought into contact with the power transmitting member and arranged such that the pressing force of the cam and an urging force of the valve spring are transmitted through the power transmitting member, and

the plunger engaging member is retained non-rotatably in a circumferential direction of the thread engagement portion in the valve mechanism.

According to this configuration, a preferable mechanical lash adjuster used in the valve mechanism of (1) can be provided.

(13) Under the configuration of (7),

According to this configuration, a preferable mechanical lash adjuster used in the valve mechanism of (6) can be provided.

Effect of the Invention

As apparent from the above description, according to the valve mechanism of the present invention, the valve clearance can automatically and reliably be adjusted.

According to the mechanical lash adjuster of the present invention, the mechanical lash adjuster preferably used in the valve mechanism can be provided.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-sectional view of an entire rocker-arm valve mechanism showing a first embodiment in which the present invention is applied to a mechanical lash adjuster of rocker-arm valve mechanism specifications.

FIG. 2 is a view of a main part of the mechanical lash adjuster according to the first embodiment, including (a) a view of lead and flank angles of a thread ridge of a male thread formed on a plunger and (b) a view of lead and flank angles of a thread ridge of a female thread formed on a housing.

FIG. 3 is an explanatory view for explaining a principle of the plunger sliding and rotating in a thread engagement portion and moving in an axial-load acting direction due to swinging of the plunger.

FIG. 4 is diagrams (a) to (d) for explaining motions of the plunger when a lateral load is input to (acts on) an upper end portion of the plunger from the near side toward the far side on the plane of the figure, including (a), (b) as the case in which the lateral load acts on the plunger while an axial load acts thereon in an extension direction and (c), (d) as the case in which the lateral load acts on the plunger while an axial load acts thereon in a contraction direction and showing (a), (c) as diagrams of the plunger viewed from the left with respect to the input (acting) direction of the lateral load and (b), (d) as diagrams of the plunger viewed from the right with respect to the input (acting) direction of the lateral load.

FIG. 5 is a diagram of a valve lift amount, the lateral load acting on the plunger, and a motion (lift loss) of the plunger when a rotation speed of an engine is low.

FIG. 6 is a longitudinal sectional view of a mechanical lash adjuster used in the valve mechanism according to the first embodiment.

FIG. 7 is a longitudinal sectional view of a mechanical lash adjuster used in the valve mechanism according to a second embodiment.

FIG. 8 is a perspective view of a torsion spring used in the mechanical lash adjuster according to the second embodiment.

MODES FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will now be described with reference to the drawings.

1. FIGS. 1 to 6 show a first embodiment. In FIG. 1 showing the first embodiment, reference numeral 1 denotes a valve mechanism of an internal combustion engine assembled to a cylinder head 11. In this embodiment, a rocker-arm valve mechanism is used as the valve mechanism 1, and the valve mechanism 1 includes as a mechanism opening and closing an intake (exhaust) port P leading to a combustion chamber S, an intake valve or an exhaust valve (hereinafter referred to as a valve) 10 opening/closing the intake (exhaust) port P, a cam 19a disposed above the valve 10, a rocker arm 16 as a power transmitting member disposed between the valve 10 and the cam 19a, and a mechanical lash adjuster (hereinafter referred to as the lash adjuster) 20 supporting the rocker arm 16.

(1-1) As is known, the valve 10 integrally includes a stem 10A, and the stem 10A is slidably inserted in a cylindrical valve sliding guide 11b retained in a through-hole leading to the intake port (or exhaust port) P. The stem 10A has a shaft end portion (in FIG. 1, an upper end portion) projected above an upper surface of the cylinder head 11 with a cotter 12a and a spring retainer 12b mounted on an outer circumference of a tip portion thereof, and a spring seat 11a is disposed on the upper surface of the cylinder head 11 under the cotter 12a and the spring retainer 12b. A valve spring (compression coil spring) 14 is wound around the outer circumference of the stem 10A in a loosely fitted state, and the valve spring 14 is interposed between the spring retainer 12b and the spring seat 11a to urge the valve 10 in the direction of closing the opening of the intake (exhaust) port P. Reference numeral 10a denotes a taper-shaped seat formed on the outer circumference of a head of the valve 10, and reference numeral 11c denotes a seat insert formed into a taper shape corresponding to the seat 10a on a circumferential edge portion of the opening of the intake (exhaust) port P to the combustion chamber S.

(1-2) The cam 19a is fixed to a camshaft 19 rotationally driven in synchronization with rotation of an automobile engine. The cam 19a is rotationally driven according to the rotation of the cam shaft 19. As is known, the outer circumferential surface of the cam 19a is made up of a base circle 19a1 and a cam nose 19a3, and the base circle 19a1 and the cam nose 19a3 are divided by an open-side ramp portion 19a21 and a close-side ramp portion 19a22, and the cam nose 19a3 is most projected at a cam top 19a4.

(1-3) The rocker arm 16 is swung based on the rotational drive of the cam 3. The rocker arm has one end side brought into contact with the shaft end portion of the stem 10A, and a socket portion 18 for supporting the lash adjuster 20 described later is formed on the other end side thereof. A roller 17b supported by a roller shaft 17a is disposed in a longitudinal middle of the rocker arm 16 and the cam 19a is brought into contact with the roller 17b. This causes the rocker arm 16 to swing by using the lash adjuster 20 as a fulcrum based on a rotational driving force of the cam 3, and the rotational driving force of the cam 19a is transmitted through the swinging of the rocker arm 16 to the stem 10A. Consequently, the stem 10A slides on the cylindrical valve sliding guide 11b, and the valve 10 opens and closes the intake port (or the exhaust port) P according to the sliding of the stem 10A.

(1-4) As shown in FIGS. 1 and 6, the lash adjuster 20 has a plunger 24 disposed in a cylindrical housing 22 serving as a plunger engaging member, and a plunger spring 26 is associated with the housing 22 and the plunger 24.

(1-4-1) The housing 22 is inserted with an opening on one end side thereof facing upward in a bore 13 formed in the upper side of the cylinder head 11 and extending in the vertical direction. Although inserted in the bore 13 such that the other end portion (lower end portion) comes into contact with a bottom surface of the bore 13, the housing 22 is not press-fitted into the bore 13 (an active housing rotation stopping means is not provided). However, when the plunger 24 is pushed down via the rocker arm 16, a friction torque is generated between the other end portion (lower end portion) of the housing 22 and the bottom surface of the bore 13, and the friction torque prevents the housing 22 from rotating relative to the bore 13. Therefore, the housing 22 is retained so as not to rotate relative to the bore 13 by the friction torque generated with the bottom surface of the bore 13.

The housing 22A has a female thread 23 formed on an inner circumferential surface thereof, and a disc-shaped spring seat surface plate 27a is accommodated non-rotatably on the other end portion side (lower end portion side) in the housing 22 such that the spring seat surface plate 27a is fixed by a C-ring 27b to the housing 22 and cannot be displaced in the axially direction thereof. A locking hole 31 for locking the plunger spring 26 described later is formed in the spring seat surface plate 27a.

(1-4-2) A rod-shaped member is used for the plunger 24. This plunger 24 has a substantially hemispherical pivot portion 24a formed on one end side and a male thread 25 formed on an outer circumferential surface on the other end side thereof. The male thread 25 is screwed into the female thread 23 on the inner circumferential surface of the housing 22 such that one end side of the plunger 24 projects outward from the opening on the one end side of the housing 22, and the pivot portion 24a enters the inside of the socket portion 18 of the rocker arm 16 and is engaged with the socket portion 18. Therefore, axial engagement is achieved between the plunger 24 on which the pressing force of the cam 19a acts as an axial load and the housing 22 retained so as not to rotate in a circumferential direction, through the male thread 25 on the plunger 24 side and the female thread 23 on the housing 22 side.

A spring housing hole 32 is formed inside the plunger 24 on the other end side thereof. The spring housing hole 32 extends in the extension direction of the plunger 24 with one end (inner end) of the spring accommodating hole 32 defined by a spring seat surface 33, and a locking hole 34 for locking the plunger spring 26 described later is formed in the spring seat surface 33. The other end of the spring housing hole 32 is opened to the outside from the other end surface of the plunger 24, and the inside of the spring housing hole 32 faces the spring seat surface plate 27a.

(1-4-3) As shown in FIGS. 1 and 6, the plunger spring 26 is interposed between the spring seat surface 33 defining the one end of the spring housing hole 32 of the plunger 24 and the spring seat surface plate 27a. In this embodiment, a spring used for the plunger spring 26 has a function as a torsion spring in addition to the function as a compression coil spring, and the plunger spring 26 is formed into a coil shape at constant pitches such that a wire rod forming the plunger spring 26 is bent at both end portions as locking portions (arms) 35, 36 toward the outside in the axial direction of the plunger spring 26. The plunger spring 26 is housed in the spring housing hole 32 with the axial direction thereof directed in the extension direction of the spring housing hole 32, and the locking portion 35 on one axial side (lower side in FIG. 1) is locked in the locking hole 31 of the spring seat surface plate 27a while the locking portion 36 on the other axial side (upper side in FIG. 1) is locked in the locking hole 34 of the spring seat surface 33. The plunger spring 26 can be twisted and released based on the relative rotation of the plunger 24 with respect to the housing 22 and can be compressed and released (extended) according to extension and contraction of the housing 22 and the plunger 24 based on the relative rotation of the plunger 24 with respect to the housing 22. In a form in which the base circle 19a1 of the cam 19a is in contact with the rocker arm 16, the plunger spring 26 urges the plunger 24 in the direction of extension from the housing 22 due to the function as a compression coil spring and urges the plunger 24 in a relative rotational direction for extension from the housing 22 due to the function as a torsion spring.

The spring force of the plunger spring 26 is obviously set weaker than the spring force of the valve spring 14.

(1-4-4) The female thread 23 on the housing 22 and the male thread 25 on the plunger 24 constitute a thread engagement portion 30 through a screwed relationship between the threads 23, 25. The thread engagement portion 30 is set such that when an axial load acts on the plunger 24 in one of extension and contraction directions, the slide rotation of the plunger 24 relative to the housing 22 is suppressed by the friction torque generated in the thread engagement portion 30 to make the threads self-sustaining (put the thread engagement portion 30 into a relatively immovable state) and that when a lateral load acts on the plunger 24, the plunger 24 is allowed to slide and rotate (the suppression of the slide rotation is relieved) and moved in the axial-load acting direction, and in this embodiment, as shown in enlarged view of FIGS. 2(a) and 2(b), the male thread 25 and the female thread 23 are each made up of a trapezoidal thread such that the thread ridges of the male thread 25 and the female thread 23 are set according to the viewpoint described above in terms of a lead angle and a flank angle.

Specifically, the thread angles of the thread ridges of the male thread 25 and the female thread 23 are set to a lead angle less than 15 degrees and a flank angle within a range of 5 to 60 degrees. The lead angle is set less than 15 degrees because if the lead angle is 15 degrees or more and the axial load acts on the plunger 24, the plunger 24 slides and rotates in the thread engagement portion 30 and makes it difficult to “reliably make the threads self-sustaining” by the friction torque generated in the thread engagement portion 30 and, in contrast, when the lead angle is less than 15 degrees, the plunger 24 having the axial load acting thereon does not slide and rotate in the thread engagement portion 30 so that the “threads is made self-sustaining” by the friction torque generated in the thread engagement portion 30. The flank angle is set within the range of 5 to 60 degrees because if the flank angle is less than 5 degrees, the substantial friction angle of the thread engagement portion 30 falls into a category of a small square thread, which makes changing the flank angle meaningless and highly-accurate machining without influence of a lead error difficult, and on the other hand, if the flank angle exceeds 60 degrees, although the “thread” is easily machined, an extremely large substantial friction angle leads to a considerable influence of lubrication oil and increases a lift loss during operation of the engine so that the thread cannot practically be used.

More specifically, a lead angle α of the thread ridge of the male thread 25 (female thread 23) and an upper flank angle θ25a (θ23a) and a lower flank angle θ25b (θ23b) of the thread ridge of the male thread 25 (female thread 23) are preferably set to, for example, the lead angle α=10 degrees, the upper flank angle θ25a, θ23a=10 degrees, and the lower flank angle θ25b, θ23b=10 degrees.

(1-4-5) Due to such setting of the thread engagement portion 30, when the intake (exhaust) port P is operated to open/close by the valve 10, the axial load acts on the plunger 24 via the rocker arm 16 during the operation in the lash adjuster 20, and the slide rotation of the plunger 24 is suppressed by the friction torque generated in the thread engagement portion 30 so that the threads in the thread engagement portion 30 are made self-sustaining and put into an immovable state. Therefore, the pivot portion 24a at the tip of the plunger 24 functions (acts) as a fulcrum of swinging of the rocker arm 16 swinging in coordination with the rotation of the camshaft 19, and the function as the fulcrum of swinging of the rocker arm 16 causes the valve 10 to reciprocate in the vertical direction, so that the lift amount of the valve 10 shows a mound shape in this case as shown in FIG. 5.

When the cam 19a presses (the roller 17b of) the rocker arm 16 and the axial load acts on the plunger 24, the contact point of the cam 19a1 with (the roller 17b of) the rocker arm 16 moves on (the roller 17b of) the rocker arm 16 and changes the acting direction of the pressing force of the cam 19a, so that a lateral load also acts on the plunger 24 as indicated by reference numerals T1, T2 of FIG. 5. When the lateral load acts on the plunger 24, the plunger 24 swings by an amount corresponding to the backlash of the thread engagement portion 30 relative to the housing 22 in the lateral-load acting direction and, at the contact point of the male thread 25 with the female thread 23, a reaction force based on the lateral load works in the direction along a flank face of the female thread 23. In this case, since the lateral-load acting direction does not coincide with the direction of the reaction force at the contact point, the reaction force at the contact point acts as a moment causing the plunger 24 to slide and rotate in the thread engagement portion 30 and the plunger 24 moves in the axial-load acting direction while sliding and rotating and eliminates a state of increased/decreased valve clearance.

2. Description will be made of the principle of the plunger 24 moving in the axial-load acting direction while sliding and rotating when the lateral load acts on the plunger 24 in more detail with reference to FIGS. 3 and 4.

(2-1) For example, as indicated by reference numeral F1 of FIG. 3, when the axial load acting on the plunger 24 is upward (e.g., in a form in which only the urging force of the plunger spring 26 acts thereon), an upper flank face 25a of the male thread 25 is in contact with a lower flank face 23b of the female thread 23. A contact point is denoted by reference numeral P1. In FIG. 3, when a lateral load T acts on the pivot portion 24a at the tip of the plunger 24 arranged in the vertical direction (see FIG. 1) from the near side toward the far side on the plane of FIG. 3, the plunger 24 uses a lower end portion of the thread engagement portion 30, i.e., a plunger lower end portion 24b (see FIGS. 1 and 4) in thread engagement with the housing-side female thread 23, as a fulcrum such that the pivot portion 24a at the tip of the plunger 24 swings from the near side toward the far side on the plane of FIG. 3.

Therefore, when the thread engagement portion 30 (male thread 25) is a normal right-hand thread, the upper flank face 25a of the male thread 25 in the left half of the male thread 25 (the left half of FIG. 3) operates to push the lower flank face 23b of the female thread 23 extending downward while turning clockwise (on the basis of the downward direction), and the upper flank face 25a of the male thread 25 in the right half of the male thread 25 (the right half of FIG. 3) operates in a direction away from the lower flank face 23b of the female thread 23 extending upward while turning clockwise (on the basis of the upward direction).

Thus, the housing-side female thread 23 is retained so as not to rotate in the circumferential direction of the thread engagement portion 30, and therefore, at the contact point P1 of the upper flank face 25a in the left half of the male thread 25 with respect to the lower flank face 23b of the female thread 23, a reaction force based on the lateral load acts in the direction along the lower flank face 23b of the female thread 23 extending upward while turning clockwise (on the basis of the upward direction). In this case, since the acting direction (input direction) of the lateral load T does not coincide with the direction of the reaction force at the contact point P1, the reaction force at the contact point P1 acts as the moment causing the plunger 24 to slide and rotate in the thread engagement portion 30 in a direction R1 of FIG. 3, and the plunger 24 moves in the acting direction of the axial load F1 (upward) while sliding and rotating by an amount corresponding to the backlash.

More specifically, in the left half of the plunger 24 with respect to the input (acting) direction of the lateral load T, as shown in FIG. 4(a), when the plunger 24 swings due to the input of the lateral load, the upper flank face 25a of the male thread 25 comes into contact with the lower flank face 23b of the housing-side female thread 23 retained so as not to rotate in the circumferential direction and can no longer operate (move leftward in FIG. 4(a)). On the other hand, in the right half of the plunger with respect to the input (acting) direction of the lateral load T, as shown in FIG. 4(b), when the plunger 24 swings due to the input of the lateral load, the upper flank face 25a of the male thread 25 moves away from the lower flank face 23b of the female thread 23 (moves rightward in FIG. 4(b)), and is no longer restrained. Consequently, the upper flank face 25a of the male thread 25 receives the reaction force from the lower flank face 23b of the housing-side female thread 23, and the plunger 24 moves in the extension direction (upward) while sliding and rotating in the direction R1 of FIG. 3 by an amount corresponding to the backlash.

From the above, for example, when the thread engagement portion 30 (male thread 25) is a normal right-hand thread and the axial load F1 acting on the plunger 24 is upward, the plunger 24 swinging due to the lateral load T moves in the acting direction of the axial load F1 (extension direction) while always rotating in the direction R1 of FIG. 3.

(2-2) On the other hand, as indicated by an arrow F2 of FIG. 3, when the axial load acting on the plunger 24 is downward (e.g., in a form in which the urging force of the valve spring 14 acts on the plunger 24 via the rocker arm 16), a lower flank face 25b of the male thread 25 is in contact with an upper flank face 23a of the female thread 23. A contact point is denoted by reference numeral P2. When the lateral load T acts on the pivot portion 24a at the tip of the plunger 24 from the near side toward the far side on the plane of FIG. 3, the plunger 24 uses the lower end portion (plunger lower end portion) 24b of the thread engagement portion 30 as a fulcrum such that the pivot portion 24a at the tip of the plunger 24 swings from the near side toward the far side on the plane of FIG. 3.

Therefore, when the thread engagement portion 30 (male thread 25) is a normal right-hand thread, the lower flank face 25b of the male thread 25 in the right half of the male thread 25 (the right half of FIG. 3) operates to push the upper flank face 23a of the female thread 23 extending upward while turning clockwise (on the basis of the upward direction), and the lower flank face 25b of the male thread 25 in the left half of the male thread 25 (the left half of FIG. 3) operates in a direction away from the upper flank face 23a of the female thread 23 extending downward while turning clockwise (on the basis of the downward direction).

Thus, the housing-side female thread 23 is retained so as not to rotate in the circumferential direction of the thread engagement portion 30, and therefore, at the contact point P2 of the lower flank face 25b in the right half of the plunger-side male thread 25 with respect to the upper flank face 23a of the housing-side female thread 23, a reaction force based on the lateral load acts in the direction along the upper flank face 23a of the female thread 23 extending downward while turning clockwise (on the basis of the downward direction). In this case, since the acting direction of the lateral load T does not coincide with the direction of the reaction force at the contact point P2, the reaction force at the contact point P2 acts as the moment causing the plunger 24 to slide and rotate in the thread engagement portion 30 in a direction R2 of FIG. 3, and the plunger 24 moves in the acting direction of the axial load F2 (downward) while sliding and rotating by an amount corresponding to the backlash.

More specifically, in the right half of the plunger 24 with respect to the input (acting) direction of the lateral load T, as shown in FIG. 4(d), when the plunger 24 swings due to the lateral load T, the lower flank face 25b of the male thread 25 comes into contact with the upper flank face 23a of the female thread 23 and can no longer operate (move rightward in FIG. 4(d)). On the other hand, in the left half of the plunger 24 with respect to the input (acting) direction of the lateral load T, as shown in FIG. 4(c), when the plunger 24 swings due to the lateral load T, the lower flank face 25b of the male thread 25 moves away from the upper flank face 23a of the female thread 23 and is no longer restrained (moving leftward in FIG. 4(c)). Consequently, the lower flank face 25b of the male thread 25 receives the reaction force from the upper flank face 23a of the housing-side female thread 23, and the plunger 24 moves in the contraction direction (downward) while sliding and rotating in the direction R2 of FIG. 3 by an amount corresponding to the backlash.

From the above, for example, when the thread engagement portion 30 (male thread 25) is a normal right-hand thread and the axial load F2 acting on the plunger 24 is downward, the plunger 24 swinging due to the lateral load T moves in the acting direction of the axial load F2 (contraction direction) while always rotating in the direction R2 of FIG. 3.

(2-3) As described above, when the lead angle and the flank angle of the thread ridges of the “threads” constituting the thread engagement portion 30 are set to predetermined values (e.g., the lead angle α=10 degrees, the upper flank angle θ25a, θ23a=10 degrees, and the lower flank angle θ25b, θ23b=10 degrees), the plunger 24 having the axial load acting thereon basically becomes relatively immovable in the thread engagement portion 30 (the threads are made self-sustaining) and functions (acts) as a fulcrum of swinging of the rocker arm 16, so that when the lateral load T acts on the plunger 24, the plunger 24 operates by an amount corresponding to the backlash of the thread engagement portion 30 not only in the extension direction of the plunger 24 (the direction of decreasing the valve clearance) but also in the contraction direction of the plunger 24 (the direction of increasing the valve clearance).

3. An operation of a valve mechanism incorporating the lash adjuster 20 will be described.

(3-1) As shown in FIGS. 1 and 5, when the cam shaft 19 (the cam 19a) rotates, the contact point of the cam 19a with (the roller 17b of) the rocker arm 16 is on the cam nose 19a3 at a cam angle from about −60 degrees to about +60 degrees and is on the base circle 19a1 of the cam 19a at the cum angle in the other range (about −60 degrees or less and about +60 degrees or more). While the cam angle is about −60 degrees to about +60 degrees, the contact point of the cam 19a with the rocker arm 16 is located on one side surface of the cam nose 19a3 from the open-side ramp portion 19a21 to the cam top 19a4 of the cam at the cam angle from about −60 degrees to 0 degrees, and the contact point of the cam 19a with the rocker arm 16 is located on the other side surface of the cam nose 19a3 from the cam top 19a4 to the close-side ramp portion 19a22 at the cam angle from 0 degrees to about +60 degrees.

(3-2) First, when the contact point of the cam 19a with the rocker arm 16 is on the base circle 19a1 of the cam 19a (when the cam angle is −60 degrees or less), a predetermined urging force of the plunger spring 26 acts on the plunger 24, and this urging force is balanced with the friction force generated on the thread engagement portion 30 (thread surfaces) so that the plunger 24 does not move in the extension/contraction direction with the valve clearance (clearance between the cam 19a and the rocker arm 16) retained at zero. Therefore, the plunger 24 becomes immovable with “threads made self-sustaining” in the thread engagement portion 30, and the lash adjuster 20 functions as the fulcrum of swinging of the rocker arm 16.

(3-3) When the contact point of the cam 19a with the rocker arm 16 is located between the open-side ramp portion 19a21 of the cam and the close-side ramp portion 19a22 on the opposite side across the cam top 19a4 (when the cam angle of FIG. 5 is in the range from −60 degrees to +60 degrees), the pressing force due to the cam 19a acts as an axial load on the plunger 24 via the rocker arm 16. Therefore, the plunger 24 becomes immovable with “threads made self-sustaining” in the thread engagement portion 30 so that the lash adjuster 20 functions as the fulcrum of swinging of the rocker arm 16, and a lift amount of the valve 10 corresponding to one rotation of the cam 19a forms a mound shape with a Max lift of about 10 mm as indicated by a broken line of FIG. 5. Although described in detailed later, because of a backlash present in the thread engagement portion 30 between the plunger 24 and the housing 22, the lift amount of the valve 10 shown in FIG. 5 includes a lift loss δ (e.g., about 0.2 mm) generated as the plunger 24 automatically slides and rotates to move in the contraction direction.

(3-4) When the pressing force from the cam 19a acts as the axial load on the plunger 24 via the rocker arm 16, since the contact point of the cam 19a with (the roller 17b) of the rocker arm 16 moves according to the rotary movement of the cam 19a and the acting direction of the pressing force on (the roller 17b of) the rocker arm 16 of the cam 19a changes, the lateral loads T1, T2 of about 250 to 150 N act on the plunger 24 as shown in FIG. 5. The valve mechanism 1 uses the lateral loads T1, T2 to adjust the positive (negative) valve clearance generated in the valve mechanism 1.

(3-4-1) When the contact point of the cam 19a with the rocker arm 16 shifts from the open-side ramp portion 19a21 to the cam nose 19a3, the positive (negative) valve clearance generated in the valve mechanism 1 is adjusted as follows.

(3-4-1-1) The positive valve clearance in the valve mechanism 1 is manifested as a gap between the cam 19a and the roller 17b of the rocker arm 16 when the contact point of the cam 19a with the rocker arm 16 is on the base circle 19a1 of the cam 19a. In this case, the urging force of the plunger spring 26 acts on the plunger 24, and this urging force is balanced with the friction force generated on the thread engagement portion 30 (thread surfaces) so that the threads of the thread engagement portion 30 are retained in the self-sustaining state.

In this state, when the contact point (contact point with a gap) of the cam 19a with the rocker arm 16 shifts from the open-side ramp portion 19a21 to the cam nose 19a3, the lateral load T1 (see FIG. 5) acts on the plunger 24 according to the shift of the contact point. This lateral load T1 acts via the rocker arm 16 on the plunger 24 in the immovable state in which the axial load acts in the extension direction due to the urging force of the plunger spring 26 immediately before the pressing force of the cam 19a acts as the axial load and, based on this action, the plunger 24 moves in the extension direction that is the axial-load acting direction. As a result, the plunger 24 pushes up the rocker arm 16 while sliding and rotating, and the positive clearance generated in the valve mechanism 1 is adjusted to zero.

Specifically, when the lateral load T1 (see FIG. 5) acts on the plunger 24 via the rocker arm 16, the plunger 24 swings by an amount corresponding to the backlash in the thread engagement portion 30 between the female thread 23 and the male thread 25 in the acting direction of the lateral load T1 on the lower end portion 24b of the plunger 24 used as the fulcrum, and the reaction force based on the lateral load works in the direction along the lower flank face 23b of the female thread 23 at the contact point P1 (see FIG. 3) of the male thread 25 with the female thread 23. The reaction force at the contact point P1 acts as the moment causing the plunger 24 to slide and rotate in the thread engagement portion 30 and the plunger 24 moves in the axial-load acting direction (the acting direction of the urging force of the plunger spring 26, the plunger extension direction) while sliding and rotating, and adjusts the positive valve clearance to zero.

(3-4-1-2) On the other hand, the negative valve clearance in the valve mechanism 1 is manifested as an excessively small gap (negative gap) between the cam 19a and the roller 17b since the rocker arm 16 (the roller 17b) is pressed by the base circle 19a1 of the cam 19a due to the urging force of the valve spring 14 when the contact point of the cam 19a with the rocker arm 16 is on the base circle 19a1 of the cam 19a. In this case, although the urging force of the valve spring 14 acts on the plunger 24 via the rocker arm 16 as the axial load in the contraction direction, this urging force is balanced with the friction force generated on the thread engagement portion 30 (thread surfaces) so that the threads of the thread engagement portion 30 are retained in the self-sustaining state.

In this state, when the contact point (negative gap) of the cam 19a with the rocker arm 16 shifts from the open-side ramp portion 19a21 to the cam nose 19a3, the lateral load T1 acts on the plunger 24 according to the shift of the contact point. This lateral load T1 acts via the rocker arm 16 on the plunger 24 in the immovable state in which only the urging force of the valve spring 14 acts as the axial load immediately before the pressing force of the cam 19a acts as the axial load and, based on this action, the plunger 24 moves in the contraction direction that is the axial-load acting direction while sliding and rotating. As a result, the cam 19a pushes down the rocker arm 16, and the negative clearance generated in the valve mechanism 1 is adjusted to zero.

Specifically, when the lateral load T1 (see FIG. 5) acts on the plunger 24 via the rocker arm 16, the plunger 24 swings by an amount corresponding to the backlash in the thread engagement portion 30 between the female thread 23 and the male thread 25 in the acting direction of the lateral load T1 on the lower end portion 24b used as the fulcrum, and the reaction force based on the lateral load works in the direction along the upper flank face 23a of the female thread 23 at the contact point P2 (see FIG. 3) of the male thread 25 with the female thread 23. The reaction force at the contact point P2 acts as the moment causing the plunger 24 to slide and rotate in the thread engagement portion 30 and the plunger 24 moves in the plunger contraction direction that is the acting direction of the axial load (the urging force of the valve spring 14) while sliding and rotating, and adjusts the valve clearance to zero.

(3-4-2) When the contact point of the cam 19a with the rocker arm 16 shifts from the cam nose 19a3 to the close-side ramp portion 19a22, the positive (negative) valve clearance generated in the valve mechanism 1 is adjusted as follows.

(3-4-2-1) First, description will be made of the case that the lateral load T2 of FIG. 5 acts on the plunger 24 when the positive valve clearance exists on the base circle 19a1 of the cam 19a.

When the contact point of the cam 19a with the rocker arm 16 (the contact point with an inherent gap) shifts from the cam nose 19a3 to the close-side ramp portion 19a22, the lateral load T2 acts on the plunger 24 according to the shift of the contact point. Specifically, as the cam 19a rotates, the pressing force of the cam 19a against the rocker arm 16 becomes weaker when the contact point of the cam 19a with the roller 17b comes closer to the close-side ramp 19a2 of the cam 19a, and a gap is generated between the cam 19a and the roller 17b (the inherent gap in the contact point is manifested) before the contact point shifts to the close-side ramp 19a2. In this state in which the pressing force of the cam 19a against the rocker arm 16 becomes weaker and the axial load acting on the plunger 24 (the reaction force of the valve spring 14) is almost eliminated immediately before the gap is generated (manifested), the lateral load T2 (see FIG. 5) acts on the plunger 24 according to the shift of the contact point of the cam 19a with the rocker arm 16. Therefore, the lateral load T2 (see FIG. 5) acts via the rocker arm 16 on the plunger 24 on which the axial load acts in the extension direction due to the urging force of the plunger spring 26, and the plunger 24 moves in the extension direction that is the axial-load acting direction. As a result, the plunger 24 pushes up the rocker arm 16 and the positive valve clearance on the base circle 19a1 of the cam 19a (positive valve clearance generated in the valve mechanism 1) is adjusted to zero.

(3-4-2-2) On the other hand, the negative valve clearance in the valve mechanism 1 is manifested as a form in which a gap is generated between the seat 10a and the seat insert 11c of the valve 10 when the valve 10 is in the state of closing the intake (exhaust) port P, i.e., when the contact point of the cam 19a with the rocker arm 16 is on the base circle 19a1 of the cam 19a. In this state, since the roller 17b of the rocker arm 16 is pressed against the cam 19a by the urging force of the valve spring 14, the urging force of the valve spring 14 acts on the plunger 24 of the lash adjuster 20 via the rocker arm 16 as the axial load in the contraction direction.

Therefore, when the lateral load T2 (see FIG. 5) acts via the rocker arm 16 on the plunger 24 on which the urging force of the valve spring 14 acts as the axial load in the contraction direction as the pressing force of the cam decreases immediately before the contact point of the cam 19a with the rocker arm 16 shifts from the cam nose 19a3 to the close-side ramp portion 19a22, the plunger 24 moves in the contraction direction that is the axial-load acting direction, and the cam 19a pushes down the locker arm 16, so that the negative valve clearance generated in the valve mechanism 1 is adjusted to zero.

(3-4-2-3) For example, if an engine is rapidly cooled after being stopped in a warmed state, the valve clearance may be put into an excessively small (negative) state due to a difference in thermal expansion coefficient between a cylinder head (aluminum alloy) and a valve (iron alloy) so that a face surface of the valve may float from a valve seat. If the valve seat surface is worn out, the same thing happens (the valve clearance is put into the excessively small state and the face surface of the valve floats from the valve seat). If the engine is started and driven in such an excessively small (negative) state of the valve clearance, the combustion chamber is not sealed and an appropriate output cannot be acquired.

However, in this embodiment, in the excessively small state of the valve clearance, the lateral load acts via the rocker arm 16 on the self-sustaining plunger 24 on which only the urging force of the valve spring 14 acts as the axial load immediately after the start of the lift of the valve or immediately before the end of the lift and, when the plunger 24 swings in the lateral-load acting direction, the reaction force works at the contact point P2 in the thread engagement portion 30 so that the moment is generated. Consequently, the plunger 24 moves in the plunger contraction direction that is the axial-load acting direction, i.e., in the direction of increasing the valve clearance, while sliding and rotating in the thread engagement portion 30, and the excessively small state of the valve clearance is eliminated.

Therefore, when the engine is driven, the combustion chamber can reliably be sealed by the valve 10 and an appropriate output can be acquired.

(3-5) Therefore, when the axial load acts on the plunger 24 as a load in one of the extension and contraction directions thereof in the valve mechanism 1 of this embodiment, the thread engagement portion 30 can be made relatively immovable (the threads are made self-sustaining) and the plunger 24 can be allowed to function as a fulcrum for swinging the rocker arm 16 and, on the other hand, when the lateral load acts on the plunger 24, the plunger 24 operates by an amount equivalent to the backlash of the thread engagement portion 30 in the direction corresponding to the acting direction of the axial load to the plunger 24 (the plunger extension direction (the direction of decreasing the valve clearance) or the plunger contraction direction (the direction of increasing the valve clearance)) so that the valve clearance is adjusted, and the adjustment of the valve clearance is implemented by utilizing only the slide rotation of the plunger 24 due to the swinging of the plunger 24 in the lateral-load acting direction based on the backlash without utilizing the structure causing the plunger 24 to slide and rotate due to the action of the axial load to the plunger 24 (the structure of Patent Document 3). Therefore, unlike the case that the valve clearance is adjusted by the structure allowing the axial load to act on the plunger 24 to cause the slide rotation of the plunger 24, the plunger is prevented from moving more than an assumed movement amount and the valve clearance can automatically and reliably be adjusted.

4. Since the backlash is present in the thread engagement portion 30 between the plunger 24 and the housing 22 of the lash adjuster 20, when the valve 10 performs a descending operation in coordination with the rotation of the cam 19a, the plunger 24 automatically moves in the contraction direction to reduce the lift amount so that the lift loss δ is generated; however, the lift loss δ is automatically eliminated by a correction function of the lash adjuster 20.

In particular, when the contact point of the cam 19a with the rocker arm 16 shifts from the open-side ramp portion 19a21 to the cam nose 19a3 of the cam 19a, both the axial load and the lateral load always act on the lash adjuster 20 as shown in FIGS. 1, 3, 4, and 5. When the lateral load T1 (see FIG. 5) acts on the plunger 24, the direction of movement thereof is determined by the axial-load acting direction. Specifically, when the contact point of the cam 19a is on the base circle 19 al of the cam 19a (when the cam angle is less than −60 degrees), the urging force of the plunger spring 26 acts on the plunger 24, and the friction force balanced with this urging force is generated on the thread surfaces of the thread engagement portion 30. Therefore, the plunger 24 is retained in the immovable state without moving in the extension/contraction direction, and the valve clearance (the gap between the cam 19a and the rocker arm 16) is maintained at zero.

Subsequently, when the contact point of the cam 19a shifts from the base circle 19a1 to the open-side ramp portion 19a21, a set load (the pressing force of the cam 19a, i.e., the urging force of the valve spring 14) F2 of the valve 10 suddenly acts on the plunger 24 as the axial load.

When the lateral load denoted by T1 in FIG. 5 acts on the plunger 24 via the rocker arm 16 while the axial load F2 in the contraction direction acts on the plunger 24, the plunger 24 swinging in the acting direction of the lateral load T1 slides and rotates in the thread engagement portion 30 so as to move in the contraction direction (upward in FIG. 5). Therefore, the socket portion 18 of the rocker arm 16 descends (the other end side of the rocker arm 16 ascends) by an amount corresponding to the movement amount of the plunger 24 in the contraction direction and the lift amount of the valve 10 decreases, resulting in the lift loss δ (see FIG. 5).

After this lift loss δ is generated, the plunger 24 can no longer swing and, therefore, the lift amount of the valve 10 gradually increases until the contact point of the cam 19a shifts to the top 19a4 of the cam nose 19a3; however, the lash adjuster 20 is retained in the contracted state and the lift loss δ is maintained as it is. While the cam 19a rotates and the lift amount of the valve 10 gradually decreases from the Max lift, the lateral load T2 (see FIG. 5) in the direction opposite to the lateral load T1 acts on the plunger 24 via the rocker arm 16; however, since the pressing force of the cam 19a (the urging force of the valve spring 14) is dominant in the axial load acting on the plunger 24, the lash adjuster 20 is kept in the contracted state regardless of the action of the lateral load T2. In other words, the value of the lateral load acting on the plunger is extremely small (almost no lateral load acts) in the vicinity of the Max lift, while the pressing force of the cam 19a (the urging force of the valve spring 14) is close to the maximum value, and therefore, the plunger 24 does not swing/slide or rotate so that the lash adjuster 20 is retained in the contracted state.

However, when the contact point of the cam 19a shifts to the close-side ramp portion 19a22 of the cam 19a, the axial load acting on the plunger 24 (the pressing force of the cam 19a, i.e., the urging force of the valve spring 14) decreases, and the urging force from the plunger spring 26 acts as the axial load F1. When the lateral load T2 acts via the rocker arm 16 in a state in which the direction of action of the axial load changes in this way, i.e., when the lateral load T2 acts on the plunger 24 on which the urging force by the plunger spring 26 acts as the axial load F1, as shown in FIGS. 4(a) and 4(b), the plunger 24 having been in the contracted state until then swings/slides and moves in the acting direction of the axial load F1 (the extension direction) and the lift loss δ disappears.

Therefore, in this embodiment, since the backlash is present in the thread engagement portion 30 between the plunger 24 and the housing 22 of the lash adjuster 20, the contact point between the rocker arm 16 and the cam 19a shifts from the open-side ramp portion 19a21 to the cam nose 19a3 of the cam 19a, the lift loss δ is generated, and when the contact point between the rocker arm 16 and the cam 19a shifts from the cam nose 19a3 to the close-side ramp portion 19a22, the lift loss δ automatically disappears.

As described above, since the valve clearance automatic adjustment function of the lash adjuster 20 allows the lash adjuster 20 to contract and extend according to the input variation of one cam rotation, the lift loss δ is always generated in the valve mechanism 1. Conversely, it is shown that if the lift loss δ is generated in the valve mechanism 1 during the normal operation of the engine, the lash adjuster 20 can correct the positive/negative variation in the valve clearance encountered during the operation of the engine.

5. Also in this embodiment, for example, even when the engine is sequentially cold-started, stopped, and cold-restarted under the valve mechanism structure as described above, the valve clearance adjustment is properly performed before the restart and, when the base circle of the cam 19a faces the rocker arm 16 at the time of the restart, the base circle is always in contact with the rocker arm 16.

(5-1) Description will be made in detail. When the engine is cold-started, the valve becomes extended due to a high-temperature exhaust gas for catalytic activation and the valve clearance is going to be in the excessively small (negative clearance) state and, therefore, to make an adjustment to a proper valve clearance, the plunger 24 deeply enters the inside of the housing 22 (the plunger contraction state) and eliminates the excessively small state of the valve clearance.

However, when the engine is stopped in the above state, the state of suppressing the slide rotation is maintained in the thread engagement portion 30 and the plunger 24 is retained in the state of having deeply entered the housing 22, so that when the engine is subsequently restarted while being cold, the valve 10 has contracted and returned to the original state and, on the other hand, the above state (the state of the plunger 24 having deeply entered the housing 22) is maintained. Therefore, although the plunger 24 attempts to extend so as to make an adjustment to a proper valve clearance, the plunger 24 cannot extend unless a lateral load acts on the rocker arm 16 due to the rotation of the cam 19a, so that the plunger 24 may not promptly return to the properly extended state. Consequently, when the base circle of the cam 19a faces the rocker arm 16 before the plunger 24 returns to the properly extended state, the clearance between both 16, 19a is in an excessively large state, and the cam 19a collisionally comes into contact at an open ramp portion thereof with the rocker arm 16 and makes an abnormal noise.

(5-2) Therefore, a spring having a function as a torsion spring is used as the plunger spring 26 in this embodiment in consideration of the problem described above and, based on the function as a torsion spring, the plunger 24 is always urged in the direction in which the plunger is extended due to rotation relative to the housing 22. As a result, the plunger 24 is relatively rotated and extended by the urging force based on the function as a torsion spring in the plunger spring 24 as long as the valve clearance exists and, when the base circle of the cam 19a faces the rocker arm 16 at the time of restart, the base circle is always in contact with the rocker arm 16. Consequently, even when the engine is sequentially cold-started, stopped, and cold-restarted under the structure as described above serving as the valve mechanism, the abnormal noise can be prevented from occurring due to collisional contact of the cam 19a with the rocker arm 16.

(5-3) Moreover, since the plunger spring 26 is made up of one spring member to serve as both a compression coil spring and a torsion spring in this embodiment, the parts count of necessary spring members can be reduced and the disposition space for arranging the spring members can be made as small as possible. Therefore, a preferable member can be provided as the spring material housed in the narrow spring housing hole 32 in the plunger 24.

6. FIGS. 7 and 8 show a second embodiment. In the second embodiment, the same constituent elements as those of the first embodiment are denoted by the same reference numerals and will not be described.

(6-1) The second embodiment shown in FIGS. 7 and 8 shows a modification example of the first embodiment. In the second embodiment, a compression coil spring 26a and a torsion spring 26b are separately independently provided as the plunger spring 26.

An ordinary spring is used as the compression coil spring 26a, and the compression coil spring 26a is interposed between the spring seat surface 33 defining one end of the spring housing hole 32 of the plunger 24 and the spring seat surface plate 27a so as to urge the plunger 24 in a direction of extension from the housing 22.

As shown in FIG. 8, a spring used as the torsion spring 26b is formed into a contact coil spring shape such that a wire rod forming the spring is bent at both end portions as the locking portions (arms) 35, 36 toward the outside in the axial direction thereof. The torsion spring 26b is disposed on the spring seat surface plate 27a on the outer circumferential side of the compression coil spring 26a with the axial direction thereof directed in the axial direction of the plunger 24, and the locking portion 35 on one axial side (lower side in FIG. 1) of the plunger spring 26 is locked in the locking hole 31 of the spring seat surface plate 27a while the locking portion 36 on the other axial side (upper side in FIG. 1) is locked to the plunger 24.

In this case, since the spring having the contact coil spring shape is used as the torsion spring 26b and, on the other hand, the extension/contraction motion (stroke) of the plunger 24 must be ensured while maintaining the torsion spring force thereof, a locking groove 37 extending relatively long in the axial direction of the plunger 24 is formed in the plunger 24 to lock the locking portion 36 in the locking groove 37, and the locking portion 37 extends relatively long in the extension/contraction direction of the plunger 24 while maintaining a locking relationship with the locking groove 37. Similar to the first embodiment, the torsion spring 26b urges the plunger 24 in the relative rotational direction for extension from the housing 22. Obviously, a value acquired by converting the spring coefficient of the torsion spring 26b into an axial load through the thread engagement portion 30 is smaller than the spring coefficient of the valve spring 14.

(6-2) Also in the second embodiment, in addition to the same effects as the first embodiment, the compression coil spring 26a and the torsion spring 26b can individually be selected from the viewpoint of the spring coefficient etc., and the springs in the valve mechanism 1 can easily be adjusted in terms of the urging force.

7. Although the embodiments have been described, the present invention includes the following forms:

(i) applying the valve mechanism or the mechanical lash adjuster according to the present invention to the direct-acting valve mechanism (FIGS. 6 and 7) and the rocker-arm valve mechanism (FIG. 8) described in the international application (PCT/2016/068045) serving as a basis of priority claim;

(ii) using the male thread 25 and the female thread 23 made up of triangular threads;

(iii) using the male thread 25 and the female thread 23 made up of trapezoidal threads or triangular threads having unequal flank angles, i.e., upper and lower flank angles different from each other;

(iv) using the male thread 25 and the female thread 23 made up of multiple threads such as those of two-threaded screws and three-threaded screws having multiple leads; and (v) configuring the backlash of the thread engagement portion 30 to change continuously or stepwise in the axial direction of the plunger 24.

EXPLANATIONS OF LETTERS OR NUMERALS

10 valve

11 cylinder head

14 valve spring

16 rocker arm (power transmitting member)

19
a cam

20 mechanical lash adjuster

22 housing (plunger engaging member)

23 female thread

24 plunger

25 male thread

26 plunger spring

26
a compression coil spring (plunger spring)

26
b torsion spring (plunger spring)

F1, F2 axial load acting on the plunger

T, T1, T2 lateral load acting on the plunger

α lead angle of a thread ridge

θ23a upper flank angle of the thread ridge of the female thread

θ23b lower flank angle of the thread ridge of the female thread

θ25a upper flank angle of the thread ridge of the male thread

θ25b lower flank angle of the thread ridge of the male thread

Valve Mechanism and Mechanical Lash Adjuster

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CPC

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Abstract

Description

Claims

Priority Claims (1)

CROSS-REFERENCE TO RELATED APPLICATION, PRIORITY CLAIM, AND INCORPORATION BY REFERENCE

PCT Information